Electrostatic spray nozzles are fairly well known in the art, and most of these nozzles are designed to spray paint or some type of solid powder or particles. Some electrostatic spray nozzles are used as fuel injectors for automobile engines. Some spray nozzles are used in pairs to spray two different liquids, thereby intermixing the various liquid droplets within a volume.
U.S. Pat. No. 4,854,506 discloses an electrostatic spraying apparatus that sprays an electrically charged liquid through a nozzle and has a charged electrode mounted adjacent the sprayhead, in which the voltage differential between the charged liquid and the adjacent electrode is sufficient to atomize the liquid. The electrode consists of a core of conducting or semiconducting material, which is covered by a sheath of a “semi-insulating” material, having a dielectric strength and volume resistivity sufficiently high to prevent sparking between the electrode and the sprayhead, and a volume resistivity sufficiently low to allow charge collected on the surface of the sheath material to be conducted through the semi-insulating material to the core. The preferred value for the volume resistivity of the sheathing material is in the range of 5×1011 and 5×1012 ohm-cms; the dielectric strength is above 15 kV/mm. The charging voltage for the liquid is about 40 kV; the electrode voltage is about 25 kV. If the semi-insulating sheathing material is removed from the electrodes, it is necessary to reduce the differential voltage to about 8 kV, which is accomplished by raising the electrode voltage to about 32 kV. In one embodiment, the sprayhead has linear atomizing edges or slots, and the sprayhead is charged to a voltage in the range of 1-20 kV, and an adjacent electrode is fixed at earth potential. Note that the electrode is still provided with a “semi-insulating” sheath.
U.S. Pat. No. 6,326,062 discloses an electrostatic spraying device that includes a control member that can attenuate the voltage gradient in the vicinity of the spray outlet to such an extent that spraying is suppressed until the device is brought within a predetermined distance of a site to be sprayed. The spray outlet mainly consists of a cartridge that encloses a strip of porous material impregnated with the liquid to be sprayed, which is fed to the tip of a nozzle, using a porous wick-type element that extends into the cartridge to allow liquid to be fed by capillary action to the tip. An annular shroud forms a housing around the tip; the housing is made of insulating material, or a semi-insulating material with a bulk resistivity in the range of 1011 to 1012 ohm-cm. The electrical charge on the outer edge of the shroud is of the same polarity as the voltage applied to the liquid emerging from the nozzle tip, and the position of the shroud's outer edge can be varied with respect to the tip of the nozzle. When the shroud approaches an earthed target, some of the potential existing on the shroud is “lost” to earth as a result of corona discharge, which thereby allows the nozzle to commence spraying. Until the shroud is within the critical distance that will induce the corona discharge, the voltage on the shroud will inhibit spraying of the liquid through the nozzle.
U.S. Pat. No. 5,938,126 discloses a powder spray coating system, which has an electrode positioned at the outlet of the nozzle. A controller detects the current to the electrode, and also detects the back current between an ion collector and ground. The controller determines the field strength if the distance changes between the spray gun and the target part that is being coated.
U.S. Pat. No. 5,725,151 discloses a fuel injector that has a “charge injecting electrode” and a “counter electrode.” A power supply is connected to both of these electrodes, which act as anode-cathode pair. The power supply imparts a charge in the fuel that is exiting the injector.
U.S. Pat. No. 5,720,436 discloses an electrostatic sprayer with a needle-shaped charging electrode in the air duct near the nozzle's discharge orifice. There is also a set of counter electrodes that remove free ions from the stream of coating material, in which the counter electrodes are upstream from the charging electrode.
Patent document EP 0 752 918 B1 discloses a discharge nozzle in the shape of a capillary tube that outputs a single jet. The tube is charged. A “field guard electrode” is also disclosed that has an adjustable screw that increases or decreases the flow of gas ions to the nozzle that will be sprayed. Another embodiment discloses a “slot nozzle” that is formed between two parallel plates. The output fluid of the slot nozzle exhibits multiple “cusp” and multiple jets, when the voltage and liquid flow rate are properly adjusted.
Patent document EP 0 671 980 B1 discloses some of the same apparatus as in the EP 0 752 918 document described above. Another embodiment is introduced in this '980 document which shows multiple nozzles in a circular pattern. There is also an embodiment that discloses a spray droplet dispenser in which there are two capillary nozzles that each spray liquid droplets toward an intermix space. The liquids being discharged from each of these capillary nozzles are different, and are also charged to opposite polarities. Therefore, these two different liquids will thoroughly intermix within the volume or space.